1. Bovine Buddies

A British study published this month reveals that individual cows form tight “best friendships” with others cows, with whom they wile away the warm afternoons chewing cud and shootin’ the bull. When a cow is taken away from her “best friend,” her stress levels increase and her milk yields decrease. “When heifers have their preferred partner with them, their stress levels…are reduced compared with if they were with a random individual,” said Krista McLennan, a grad student at Northampton University who discovered the correlation.

2. Holy Midwives, Batman!

Researchers studying wild Bechstein's bats found that, like cows, female bats choose specific companions with whom they roost and, um, hang out with. These friendships can last years and sometimes a lifetime, according to a study published earlier this year in the Proceedings of the Royal Society B. Some female bats were even found to act as midwives for their friends. In one documented case, a female fruit bat in Florida “repeatedly groomed and hugged [another, unrelated] pregnant bat during her pregnancy,” according to an article in Discovery News. The attending bat, along with another friend, then later fanned the mother with their wings.

3. Pachyderm’s Dilemma

Elephant friends are able to outwit a rudimentary version of the Prisoner’s Dilemma, the famous problem in game theory. According to researchers from Emory University and the Thai Elephant Conservation Center in Thailand, elephants were able to figure out that if they worked together, pulling two ends of the same piece of rope simultaneously, they’d get a treat, whereas if one elephant pulled the rope without the other’s participation, neither elephant was rewarded. In both the wild and captivity, elephants have long been observed to form close, sometimes life-long friendships with other elephants, eating together, bathing together and—in a uniquely pachydermy show of love—draping their ears and trunks over a friend’s head, trunk, or back.

4. You Scratch My Back, I’ll Scratch Yours

Both male and female chimpanzees often form long-term friendships with other chimps of their own sex to whom they are unrelated. Chimp pals generally do what human pals do: they share food, hang out together, take naps, patrol their surroundings and—perhaps most importantly—groom one another. Whether two chimp friends groom each other for roughly the same amount of time per day is a primary indicator of how long their friendship will last. Male friendships tended to last about seven years, according to a University of Michigan study, but other chimp friendships can last a lifetime.

During times of high stress, chimp friends often seek comfort and reassurance from one another, petting, hugging and expressing sympathy for their pals.

5. (Dolphin) Ladies Night

Friendships among female dolphins look a lot like friendships among female humans out for a night on the town. Like any good girlfriend, female dolphins protect their friends from inappropriate male dolphins attempting to breed with them, and from sharks and other predators, according to a recent study published in the Proceedings of the National Academy of Sciences.

Male dolphins also—perhaps not surprisingly, given the social anthropology of a nightclub—travel with a wingman or two. One of the primary roles these tight-knit male duos and trios play is to help their buddies mate with a female before she can swim away.